We present a new computational approach that addresses the difficulty of obtaining the correct interaction between
the solar corona and the transition region in response to rapid heating events. In the coupled corona/transition region/chromosphere
system, an enhanced downward conductive flux results in an upflow (chromospheric evaporation).
However, obtaining the correct upflow generally requires high spatial resolution in order to resolve the transition region.
With an unresolved transition region, artificially low coronal densities are obtained because the downward heat
flux “jumps” across the unresolved region to the chromosphere, underestimating the upflows. Here, we treat the lower
transition region as a discontinuity that responds to changing coronal conditions through the imposition of a jump
condition that is derived from an integrated form of energy conservation. To illustrate and benchmark this approach
against a fully resolved one-dimensional model, we present field-aligned simulations of coronal loops in response to a
range of impulsive (spatially uniform) heating events. We show that our approach leads to a significant improvement in
the coronal density evolution than just when using coarse spatial resolutions insufficient to resolve the lower transition
region. Our approach compensates for the “jumping” of the heat flux by imposing a velocity correction that ensures
that the energy from the heat flux goes into driving the transition region dynamics, rather than being lost through
radiation. Hence, it is possible to obtain improved coronal densities. The advantages of using this approach in both
one-dimensional hydrodynamic and three-dimensional magnetohydrodynamic simulations are discussed.